.content{
    width: 640px;
    height: 640px;
    margin: 100px auto;
    position: relative;
}
.btn{
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    background-color: rgba(0, 0, 0, .3);
    z-index: 2;
}
/* 公共的样式 */
.btn button{
    background: none;
    border: none;
    background-size: 100% 100%;
    cursor: pointer;
    outline: none;

    position: absolute;
    left: 50%;
    top: 50%;
}

/* 定义开始按钮 */
.stratBtn button{
    width: 200px;
    height: 80px;
    background-image: url(../images/startGame.png);
    /* 让按钮到中间来显示 */
    margin-left: -100px;
    margin-top: -40px;
}
.pauseBtn button{
    width: 70px;
    height: 70px;
    background-image: url(../images/start.png);
    margin-left: -35px;
    margin-top: -35px;
}
.pauseBtn{
    display: none;
}

/* 定义贪吃蛇 */
#snakeWrap{
    width: 600px;
    height: 600px;
    background-color: #225675;
    border:20px solid #7dd9ff;
    position: absolute;
}
/* #snakeWrap div{
    width: 20px;
    height: 20px;
} */
.snakeHead{
  background-image: url(../images/snake.png);
  background-size:cover;
}
.snakeBody{
    background-color:#9ddbb1;
    border-radius: 50%;
}
.food{
    background-image: url(../images/food.png);
    background-size: cover;
}